This invention relates to films containing lyotropic polybenzazole polymers and processes for coagulating and washing them.
Polybenzazole polymers are typically synthesized by polymerization in nonoxidizing dehydrating acid solutions to form viscous dopes which are solutions of the polymer in the solvent acid. Uniaxially oriented film may be synthesized from these dopes by extruding onto a rotating drum that draws the film in the machine direction and rotates it down into a water bath to coagulate. Biaxially oriented films are synthesized by extruding the dope as a tube, which is blown or forced over a mandrel to impart some biaxial orientation, and is then immersed in water to coagulate it. Examples of such processes are described in: Chenevey, U.S. Pat. No. 4,487,735 (Dec. 11, 1984); Lusignea et al.,U.S. Pat. No. 4,871,595 (Oct. 3, 1989); Chenevey, U.S. Pat. No. 4,898,924 (Feb. 6, 1990); Harvey et al., U.S. Pat. No. 4,939,235 (Jul. 3, 1990); Harvey et al., U.S. Pat. No. 4,963,428 (Oct. 16, 1990); Lusignea et al., U.S. Pat. No. 4,966,806 (Oct. 30, 1990); and Fujiwara, Japanese Kokai 63(1988)-74612 (published Apr. 5, 1988), which are incorporated herein by reference.
Once the polybenzazole dope film has been formed it must undergo coagulation in order to separate the polybenzazole from its solvent. Coagulation is the process in which a polymer in solution is contacted with a polymer nonsolvent, known as a coagulant, causing phase separation of the polymer into a gelled moiety. A coagulated film has a macroscopic structure that is essentially fixed. After the film has been coagulated it can be further washed in order to remove even more of the acid solvent. The amount of washing the film is subjected to depends upon the desired level of residual acid solvent in the final film.
The coagulated films and sheets may be used in structural materials or electronic components as described in U.S. Pat. No. 4,871,595 (Oct. 3, 1989) and 11 Ency. Poly. Sci. & Eng., Polybenzothiazoles and Polybenzoxazoles, 601 (J. Wiley & Sons 1988), which are incorporated herein by reference.
It is necessary to coagulate and wash a dope film to obtain a polybenzazole film with a desired level of residual solvent in order to produce marketplace quality polybenzazole film.